Solution of Chapter 5. States of Matter (Chemistry - Exemplar Book)

A person living in Shimla observed that cooking food without using a pressure cooker takes more time. The reason for this observation is that at high altitude:

Which of the following property of water can be used to explain the spherical shape of rain droplets?

A plot of volume (V) versus temperature (T) for a gas at constant pressure is a straight line passing through the origin. The plots at different values of pressure are shown in Fig. 5.1. Which of the following order of pressure is correct for this gas?

The interaction energy of the London force is inversely proportional to the sixth power of the distance between two interacting particles but their magnitude depends upon

Dipole-dipole forces act between the molecules possessing permanent dipole. Ends of dipoles possess ‘partial charges’. The partial charge is

The pressure of a 1:4 mixture of dihydrogen and dioxygen enclosed in a vessel is one atmosphere. What would be the partial pressure of dioxygen?

As the temperature increases, the average kinetic energy of molecules increases. What would be the effect of the increase of temperature on pressure provided the volume is constant?

Gases possess characteristic critical temperature which depends upon the magnitude of intermolecular forces between the particles. Following are the critical temperatures of some gases.

Gases H2 He O2 N2

The critical temperature

in Kelvin 33.2 5.3 15 4.3 126

154.3

From the above data what would be the order of liquefaction of these gases? Start writing the order from the gas liquefying first

What is SI unit of viscosity coefficient (η)?

Atmospheric pressures recorded in different cities are as follows:

Consider the above data and mark the place at which liquid will boil first.

Which curve in Fig. 5.2 represents the curve of ideal gas?

Increase in kinetic energy can overcome intermolecular forces of attraction. How will the viscosity of liquid be affected by the increase in temperature?

How does the surface tension of a liquid vary with increase in temperature?

With regard to the gaseous state of matter which of the following statements are correct?

Which of the following figures does not represent 1 mole of dioxygen gas at STP?

Under which of the following two conditions applied together, a gas deviates most from the ideal behaviour?

Which of the following changes decrease the vapour pressure of water kept in a sealed vessel?

If 1 gram of each of the following gases is taken at STP, which of the gases will occupy (a) greatest volume and (b) smallest volume?

CO, H₂O, CH₄, NO

Physical properties of ice, water and steam are very different. What is the chemical composition of water in all the three states.

The behaviour of matter in different states is governed by various physical laws. According to you what are the factors that determine the state of matter?

Use the information and data given below to answer the questions (a) to (c):

• Stronger intermolecular forces result in higher boiling point.

• Strength of London forces increases with the number of electrons in the molecule.

• Boiling point of HF, HCl, HBr and HI are 293 K, 189 K, 206 K and 238 K respectively.

(a) Which type of intermolecular forces are present in the molecules HF, HCl, HBr and HI?

(b) Looking at the trend of boiling points of HCl, HBr and HI, explain out of dipole-dipole interaction and London interaction, which one is predominant here.

(c) Why is boiling point of hydrogen fluoride highest while that of hydrogen chloride lowest?

What will be the molar volume of nitrogen and argon at 273.15K and 1 atm?

A gas that follows Boyle’s law, Charles law and Avogadro’s law is called an ideal gas. Under what conditions a real gas would behave ideally?

Two different gases ‘A’ and ‘B’ are filled in separate containers of equal capacity under the same conditions of temperature and pressure. On increasing the pressure slightly the gas ‘A’ liquefies but gas B does not liquefy even on applying high pressure until it is cooled. Explain this phenomenon.

Value of universal gas constant (R) is same for all gases. What is its physical significance?

One of the assumptions of kinetic theory of gases states that “there is no force of attraction between the molecules of a gas.” How far is this statement correct? Is it possible to liquefy an ideal gas? Explain.

The magnitude of surface tension of liquid depends on the attractive forces between the molecules. Arrange the following in increasing order of surface tension:

Water, alcohol (C₂H₅OH) and hexane [CH₃(CH₂)₄CH₃)].

Pressure exerted by saturated water vapour is called aqueous tension. What correction term will you apply to the total pressure to obtain pressure of dry gas?

Name the energy which arises due to motion of atoms or molecules in a body. How is this energy affected when the temperature is increased?

Name two intermolecular forces that exist between HF molecules in liquid state.

One of the assumptions of kinetic theory of gases is that there is no force of attraction between the molecules of a gas. State and explain the evidence that shows that the assumption is not applicable for real gases.

Compressibility factor, Z, of a gas is given as Z = PV/ nRT

(i) What is the value of Z for an ideal gas?

(ii) For real gas what will be the effect on value of Z above Boyle’s temperature?

The critical temperature (T _c) and critical pressure (P_c) of CO₂ are 30.98°C and 73atm respectively. Can CO₂(g) be liquefied at 32°C and 80atm pressure?

For real gases the relation between p, V and T is given by van der Waals equation:

P + an²(V - nb) / V²= nRT

Where‘a’ and ‘b’ are van der Waals constants, ‘nb’ is approximately equal to the total volume of the molecules of a gas.

‘a’ is the measure of magnitude of intermolecular attraction.

(i) Arrange the following gases in the increasing order of ‘b’. Give reason. O₂, CO₂, H₂, He

(ii) Arrange the following gases in the decreasing order of magnitude of ‘a’. Give reason. CH₄, O₂, H₂

The relation between pressure exerted by an ideal gas (P_ideal) and observed pressure (P_real) is given by the equation:

P_ideal = P_real+

If pressure is taken in Nm^-2, number of moles in mol and volume in m³, Calculate the unit of ‘a’.

What will be the unit of ‘a’ when pressure is in atmosphere and volume in dm³?

Name two phenomena that can be explained on the basis of surface tension.

Viscosity of a liquid arises due to strong intermolecular forces existing between the molecules. Stronger the intermolecular forces, greater is the viscosity. Name the intermolecular forces existing in the following liquids and arrange them in the increasing order of their viscosities. Also give reason for the assigned order in one line.

Water, hexane (CH₃CH₂CH₂CH₂CH₂CH₃), glycerine (CH₂ OH CH(OH) CH₂ OH)

Explain the effect of increasing the temperature of a liquid, on intermolecular forces operating between its particles, what will happen to the viscosity of a liquid if its temperature is increased?

The variation of pressure with volume of the gas at different temperatures can be graphically represented as shown in Fig. 5.3. On the basis of this graph answer the following questions.

(i) How will the volume of a gas change if its pressure is increased at constant temperature?

(ii) At a constant pressure, how will the volume of a gas change if the temperature is increased from 200K to 400K?

Fig. 5.3.

Pressure versus volume graph for a real gas and an ideal gas are shown in Fig. 5.4. Answer the following questions on the basis of this graph.

(i) Interpret the behaviour of real gas with respect to ideal gas at low pressure.

(ii) Interpret the behaviour of real gas with respect to ideal gas at high pressure.

(iii)Mark the pressure and volume by drawing a line at the point where real gas behaves as an ideal gas.

Match the graphs between the following variables with their names:

Match the following gas laws with the equation representing them.

Match the following graphs of ideal gas with their co-ordinates:

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): Three states of matter are the result of balance between intermolecular forces and thermal energy of the molecules.

Reason (R): Intermolecular forces tend to keep the molecules together but thermal energy of molecules tends to keep them apart.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): At constant temperature, pVvs V plot for real gases is not a straight line.

Reason (R): At high pressure all gases have Z > 1 but at intermediate pressure most gases have Z < 1.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): The temperature at which vapour pressure of a liquid is equal to the external pressure is called boiling temperature.

Reason (R): At high altitude atmospheric pressure is high.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv)A is false but R is true.

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): Gases do not liquefy above their critical temperature, even on applying high pressure.

Reason (R): Above critical temperature, the molecular speed is high and intermolecular attractions cannot hold the molecules together because they escape because of high speed.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv)A is false but R is true.

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): At critical temperature liquid passes into gaseous state imperceptibly and continuously

Reason (R): The density of liquid and gaseous phase is equal to critical temperature.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question.

Assertion (A): Liquids tend to have maximum number of molecules at their surface.

Reason (R): Small liquid drops have spherical shape.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

iv) A is false but R is true.

Isotherms of carbon dioxide at various temperatures are represented in Fig. 5.5. Answer the following questions based on this figure.

(i) In which state will CO₂ exist between the points a and b at temperature T₁?

(ii) At what point will CO₂ start be liquefying when temperature is T₁?

(iii) At what point will CO₂ be completely liquefied when temperature is T₂.

(iv) Will condensation take place when the temperature is T₃.

(v) What portion of the isotherm at T₁represent liquid and gaseous CO₂ at equilibrium?

The variation of vapour pressure of different liquids with temperature is shown in Fig. 5.6.

(i) Calculate graphically boiling points of liquids A and B.

(ii) If we take liquid C in a closed vessel and heat it continuously. At what temperature will it boil?

(iii) At high altitude, atmospheric pressure is low (say 60 mm Hg). At what temperature liquid D boils?

Pressure cooker is used for cooking food at hill station. Explain in terms of vapour pressure why is it so?

(iv) Pressure cooker is used for cooking food at hill station. Explain in terms of vapour pressure why is it so?

Why does the boundary between liquid phase and gaseous phase disappear on heating a liquid upto critical temperature in a closed vessel? In this situation what will be the state of the substance?

Why does sharp glass edge become smooth on heating it upto its melting point in a flame? Explain which property of liquids is responsible for this phenomenon.

Explain the term ‘laminar flow’. Is the velocity of molecules same in all the layers in laminar flow? Explain your answer.

Isotherms of carbon dioxide gas are shown in the given Fig 5.7. mark a path for changing gas into liquid such that only one phase (I.e., either a gas or liquid) exists at any time during the change. Explain how the temperature, volume and pressure should be changed to carry out the change.